The invention relates to a metallizable, heat-sealable, biaxially oriented multi-layer film which comprises a base layer comprising polypropylene, a first polyolefinic heat-sealable surface layer and a second polyolefinic metallizable surface layer.
EP-A No. 0,023,389 describes a coextruded multi-layer film for metallizing applications which comprises a core layer essentially of polypropylene, which has outer layers of an ethylene-olefin copolymer on both sides, the ethylene content being 85 to 99.75% by weight and the molecule of the alpha olefin containing 3 to 6 carbon atoms. This film has the disadvantage that its scratch resistance is in need of improvement and its gloss is unsatisfactory.
Moreover, EP-A No. 0,021,672 describes a laminate produced by coextrusion, comprising a polypropylene core layer and an ethylene-propylene copolymer on at least one external side of the core layer. The outer layer contains 2 to 4% by weight of ethylene, outer layers with 2.5 to 3.5% by weight of ethylene being particularly preferred. A good adhesion between the outer layer and an applied metal layer is achieved by omitting lubricants, particularly fatty acid amides, from the film. However, this film is still in need of improvement, particularly with regard to the metal adhesion, its scratch resistance and its optical properties.
DE-A No. 3,701,307 describes heat-sealable multi-layer films for metallizing applications whose metallizable surface layer is of polypropylene. These films have the disadvantage that they cannot readily be surface treated, i.e., that they have a poor long-term metallizability, since their affinity for metals, achieved by surface treatment, significantly and detectably subsides even after a short time.